Demands for services using radio communications have increased. However, frequency bands that are suitable in terms of transmission characteristics and development of devices have been occupied. Thus, secondary users desiring to provide new services use radio cognitive technology to detect unused frequency channels through temporal and/or specific inspections of frequency channels allowed to primary users so as to use the unused frequency channels. In this case, primary and secondary users refer to communication systems operated by different services or businesses. Primary users correspond to incumbent users (IUs), and secondary users correspond to users of cognitive radio systems.
The IEEE802.22 standard desires to provide data, voice(VoIP) and audio/video services in frequency bands used in televisions (TVs) (e.g., a band from 54 MHz to 698 MHz corresponding to U.S. TV channels 2 through 51 or an international band from 41 MHz to 910 MHz) using times and spaces, which are not used by primary users of televisions (TVs) or radio devices. In order to use an allocated TV frequency band in an IEEE802.22 system (a base station (BS), customer premises equipment (CPE), or a core network), a BS and CPE of a secondary user must know about the current state of a channel. For this purpose, the BS and CPE of the secondary user must scan a band from 41 MHz to 910 MHz in order to monitor the use state of the channel, wherein the band is a current TV channel. Thus, the channel can be changed to another channel when a primary user desires to use the channel while the secondary user is using the channel.
The IEEE802.22 system uses a plurality of broadcast channel bands each having a bandwidth of 6, 7, or 8 MHz within the band from 41 MHz to 910 MHz allocated to a TV broadcast. In detail, a BS and CPE of the IEEE802.22 system use a currently unused broadcast channel band of the plurality of broadcast channel bands. In other words, the IEEE802.22 system accesses each broadcast channel band.
In the present specification, a fraction of a broadcast channel band is referred to as a fractional band to describe a method and a system for using a flexible bandwidth in a cognitive radio system.
In an existing cognitive radio system, if a system of a primary user uses a fraction of a bandwidth of a broadcast channel a system of a secondary user may not use most of the broadcast channel band except for the fraction of the bandwidth. For example, if a 200 kHz narrowband radio device uses a broadcast channel band having a bandwidth of 6 MHz, systems of secondary users may not use a bandwidth of 5.8 MHz of the broadcast channel band. In this case, a band having bandwidths of 200 kHz and 5.8 MHz corresponds to the above-described fractional band.
The efficiency of a cognitive radio system depends on whether a currently unused channel is effectively detected so as to appropriately select a service suitable for the currently unused channel and provide the service to a secondary user. In other words, the efficiency of the cognitive radio system depends on how much a confined channel bandwidth is effectively used. Thus, according to existing cognitive radio systems, a bandwidth of 5.8 MHz corresponding to 96.6% of a broadcast channel bandwidth of 6 MHz is not used and is thus inefficient.